We may carry this farther, and remark, not only that two objects are connected by the relation of cause and effect, when the one produces a motion or any action in the other, but also when it has a power of producing it. And this we may observe to be the source of all the relations of interest and duty, by which men influence each other in society, and are placed in the ties of government and subordination. A master is such a one as, by his situation, arising either from force or agreement, has a power of directing in certain particulars the actions of another, whom we call servant. A judge is one, who, in all disputed cases, can fix by his opinion the possession or property of any thing betwixt any members of the society. When a person is possessed of any power, there is no more required to convert it into action, but the exertion of the will; and _that_ in every case is considered as possible, and in many as probable; especially in the case of authority, where the obedience of the subject is a pleasure and advantage to the superior. These are, therefore, the principles of union or cohesion among our simple ideas, and in the imagination supply the place of that inseparable connexion, by which they are united in our memory. Here is a kind of _attraction_, which in the mental world will be found to have as extraordinary effects as in the natural, and to show itself in as many and as various forms. Its effects are every where conspicuous; but, as to its causes, they are mostly unknown, and must be resolved into _original_ qualities of human nature, which I pretend not to explain. Nothing is more requisite for a true philosopher, than to restrain the intemperate desire of searching into causes; and, having established any doctrine upon a sufficient number of experiments, rest contented with that, when he sees a farther examination would lead him into obscure and uncertain speculations. In that case his inquiry would be much better employed in examining the effects than the causes of his principle. Amongst the effects of this union or association of ideas, there are none more remarkable than those complex ideas, which are the common subjects of our thoughts and reasoning, and generally arise from some principle of union among our simple ideas. These complex ideas may be divided into _relations, modes,_ and _substances_. We shall briefly examine each of these in order, and shall subjoin some considerations concerning our _general_ and _particular_ ideas, before we leave the present subject, which may be considered as the elements of this philosophy. SECTION V. OF RELATIONS.